In the typical milking machine, a teat cup cluster is attached to the udder of the cow during the milking process. The cluster includes four teat cups, one for each of the four quarters of the cow's udder, with each teat cup including a rigid outer shell, typically made of stainless steel, and a soft rubber or plastic inflation which fits within the shell. The inflation is connected to a line that typically leads to a common receptacle or claw which holds milk drawn from each of the four teat cups. The claw is connected by a hose to a milk line which, during the milking operation, is placed under a constant vacuum draw. The space between the rubber inflation and the metal shell of each teat cup is closed off from the outside atmosphere and is connected by a hose to a pulsator unit (usually through a manifold to which hoses extending to the other teat cups are also connected). The pulsator alternately applies vacuum and ambient air pressure to the hose(s) leading to the teat cups so that the teat cup inflations are opened to the milking vacuum in a pulsed manner to provide the appropriate milking action.
In pipeline milking systems and in modern milking parlors, common vacuum lines extend from a large vacuum pump to the milking stations where cows are milked. A pulsator is typically located at each milking station and is connected to the common vacuum line. When the pulsator switches to release the vacuum on the teat cups, it opens up the hose leading to the teat cups to the outside atmosphere so that the inflations relax and cut off the vacuum from the milk line. This generally results in air being drawn in through the pulsator into the hose leading to the teat cups. A filter or screen is thus typically provided at the air inlet to the pulsator to filter out dust, dirt, flies or other insects, and moisture. Although a modern milking parlor is relatively free of dust and insects, moisture in the air is very common because of the volume of water used for washing the cows during preparation and for washout of the equipment after milking. Where individual filters are used at each pulsator, such filters tend to become clogged or saturated with moisture relatively quickly, requiring frequent cleaning or replacement by the operator if the pulsators are to be maintained in proper working order. As an alternative to having individual filters or screens at each pulsator, many modern milking parlors have a separate ambient air line, mounted adjacent to the vacuum line to which the pulsator is connected, to receive ambient air. The common air line receives air through a large air filter typically located at a position well away from the milking stations at which the cows are being milked. Although the use of a common air line in this manner is effective, it has certain disadvantages, including the cost of installing the common air line and the connecting lines from each pulsator to the common line, space constraints in the milking parlor because of the space occupied by the common air line, some restriction in the free air flow to the pulsators through the main filter and the common air line, and the need to properly maintain the large air filter connected to the common air line. Because air is drawn in through the common air line filter to supply many pulsators, the common air filter can clog or saturate fairly rapidly, and if that air filter is not functioning properly, the performance of all of the pulsators will suffer.